Straw and other fibrous agricultural materials have traditionally been baled by feeding a column of the material into a bale chamber and compacting successive charges with a reciprocating plunger. During development of balers of conventional size, that is those with chamber cross-sections of about 350.times.450 mm, the plunger speeds have increased from 61 to around 100 strokes per minute, and although peak torque loadings have been smoothed, they are still very uneven.
The new generation of large balers which make bales with dimensions of up to 1400.times.1200 mm in cross-section still use a plunger, albeit reciprocating more slowly at 25-60 strokes per minute. Bales formed by plunger compacting machines are comprised of wads which make the bale easy to dismantle when subsequently used.
The potential of straw as a raw material is attractive if the cost of transporting and storage can be reduced. One approach is to package it in high density bales with a bulk density above 200 kg/m.sup.3, another is to form it into high density briquettes with a bulk density of over 300 kg/m.sup.3. Machines currently being developed to pack crop to these high densities require a pre-densification stage to pack the crop to about 100 kg/m.sup.3.